The invention concerns an under-the-floor lathe for re-machining the wheels in railroad-vehicle wheel sets that has two assemblies for each wheel in the set, each assembly comprising an upright, a swiveling head, an axle-bearing support, a hold-down, two friction rollers that can be positioned against one of the wheels, and a friction-roller holder, whereby at least one of the friction rollers in each holder is powered and whereby each holder rotates around an axis that travels along the mid-plane of the lathe.
An under-the-floor lathe of the aforesaid type is known from German Pat. No. 2 937 751 C2.
The machining action of a lathe of this type is accelerated by several brakes that engage the friction-roller holders to make it more difficult for the holders to pivot while the wheels are being reground.
The brakes that engage the friction-roller holders, however, are considered drawbacks in that they are rather expensive.